Mercury-cadmium-telluride (HgCdTe) photodiodes are typically fabricated in two dimensional arrays and include a layer of passivation applied to a surface of the array, the passivation layer comprising low-temperature photochemical SiO.sub.2, evaporated ZnS, or anodically grown CdS. While suitable for some imaging applications it has been found that during certain subsequent processing steps of the array, such as a 100.degree. C., high vacuum bake cycle required to outgas a vacuum Dewar which houses the photodiode array, that such a conventional passivation layer may be disadvantageous. For example, there has been observed a degradation in critical performance parameters such as diode impedance, quantum efficiency, noise (especially at low frequencies), spectral response, and optical area. This degradation is especially evident in long-wavelength detectors. Porosity of the passivation layer and lack of adhesion to the underlying HgCdTe surface are also common problems observed with the aforedescribed conventional passivation layers.
Furthermore, inasmuch as these conventional passivation materials form no more than a coating upon the HgCdTe surface, control over the HgCdTe/passivation interface band structure or energy levels is difficult or impossible to achieve. It is therefore necessary that these passivation materials both create and maintain flatband conditions at the HgCdTe/passivation interface if the array is to maintain a desired level of performance parameters, especially during and after high temperature processing and storage.
Also, conventional fabrication methods for planar arrays of photodiodes typically employ multiple photomask layers in conjunction with ion implantation to form p-n junctions. The steps of these fabrication methods are typically required to be carried out in different types of processing equipment, resulting in increased manufacturing time and cost. The required alignment of the multiple masks and the tolerances associated therewith further results in a minimum achievable junction size which may be larger than desired. Also, the use of multiple masks typically results in a nonoptimum registration between the interface between the photodiode junction, and its associated depletion region, with the overlying surface passivation layer, thereby resulting in increased diode noise currents and reduced yield due to misalignment of mask levels.